Some related background is set forth in U.S. Pat. No. 4,135,885, "Burning and Desulfurizing Coal", the contents of which are herein incorporated by reference.
Coal burners with fluid bed desulfurization using sorbents such as limestone are known in the prior art. However, these prior art devices have not been adequately satisfactory. They have been characterized by inefficient use of sorbents, inadequate removal of sulfur except at the expense of uneconomical inefficient use of sorbents, and inability to make use of many available sorbent materials. Using softer limestones resulted in fragmentation and blowing away before adequately reacting; using harder limestones resulted in sulfate coating that reduced reactivity. Also, the large particle size limestone discharged in prior art devices has caused designers to use increased steam tube spacing, with consequent increased boiler costs.